The present invention relates to a hydrosilylation method using a hydroxylated oxide of silicon or aluminum having chemically combined platinum atoms. More particularly, the present invention relates to a platinum catalyst having platinum atoms anchored onto the surface of a hydroxylated oxide of silicon or aluminum through platinum sulfur linkages.
Prior to the present invention hydrosilylation reactions, that is a reaction between silicon hydride and aliphatically unsaturated organic material to produce a silicon-carbon bond, were generally performed in the presence of an unsupported platinum catalyst such as Speier et al, J. Am. Chem. Soc., 1957, 79, 974, or Karstedt, U.S. Pat. Nos. 3,715,334 and 3,775,452, assigned to the same assignee as the present invention. Although valuable hydrosilylation results were often achieved using such unsupported platinum catalyst, it was difficult to recover platinum values upon completion of the hydrosilylation reaction. In addition, the platinum catalyst could not be reused after the reaction, as the platinum was generally in the form of the free metal which was catalytically less reactive and difficult to salvage.
As reported by Capka et al, Hydrosilylation Catalyzed by Transition Metal Complexes Coordinately Bound to Inorganic Supports, Institute of Chemical Process Fundamentals, Czechoslovak Academy of Sciences, Collection Czechoslov. Chem. Commun. (Vol. 39, 1974, pages 154-166), transition metal complexes bound to inorganic materials provide many advantages over unsupported catalysts of the prior art. It is further reported by Z.M. Michalska, Catalytic Activity of Supported Rhodium(I) and Platinum(0) Complexes in Hydrosilylation, J. of Molecular Catalysis, 3 (1977/78) 125-134, that improved catalyst performance can be achieved in olefin hydrosilylation reactions using certain complexes, for example, chloro-tris(triphenylphosphine)rhodium(I) or tetra-kis(triphenylphosphine)platinum(0) attached to the surface of a silica support containing bound diphenylphosphine groups via a ligand exchange reaction. A catalyzed oxidation of 1-hexene by dioxogen using a monomeric organosulfide-rhodium carbonyl complex chemically bound to silica gel is reported by Eric D. Nyberg et al, J. Am. Chem. Soc., 1981, 103, 496-498. Although improved results have been achieved in the art using various supported metallic catalysts as compared to results using such catalysts free of such support, continuous investigation is being made to further evaluate the effectiveness of various substrates and types of attachment of active transition metal atoms, such as platinum, to the supporting substrate.
The present invention is based on the discovery that improved performance can be achieved with a platinum catalyst in hydrosilylation reactions by utilizing as the platinum catalyst, a hydroxylated oxide of silicon or aluminum having platinum atoms anchored to the surface of the hydroxylated oxide of silicon or aluminum through siloxyorganosulfur bonds by platinum-sulfur linkages. More particularly, the platinum atoms can be anchored to the surface of the hydroxylated oxide of silicon or aluminum by platinum-sulfur linkages by ##STR1## groups, where R is a divalent C.sub.(2-13) organo radical, attached to the hydroxylated silicon oxide or aluminum oxide surface by siloxane linkages. This result is quite surprising, because experience has shown that sulfur containing materials generally adversely affect the catalytic activity of the platinum catalyst in hydrosilylation reactions.